The plating of articles with a composite coating bearing finely dispersed divided particulate matter is well documented. This technology has been widely practiced in the field of electroplating as well as electroless plating. The acceptance of such composite coating stems from the recognition that the inclusion of finely divided particulate matter within metallic matrices can significantly alter the properties of the coating with respect to properties such as wear resistance, lubricity, corrosion resistance and appearance.
Electroless composite technology is a more recent development as compared to electrolytic composite technology. The state of the art in composite electroless plating is documented in a recent text entitled "Electroless Plating Fundamentals and Applications," edited by G. Mallory and J. B. Hajdu, Chapter 11, published by American Electroplaters and Surface Finishers Society, Orlando, Fla., (1990).
The evolution of composite electroless plating dates back to Oderkerden U.S. Pat. No. 3,614,183 in which a structure of composite electroless plating with finely divided aluminum oxide was interposed between electrodeposited layers to improve the corrosion resistance. Thereafter, Metzger et al, U.S. Pat. Nos. 3,617,363 and 3,753,667 extended the Oderkerken work to a great variety of particles and miscellaneous electroless plating baths. Thereafter, Christini et al in Reissue Patent 33,767 further extended the composite electroless plating to the codeposition of diamond particles. In addition, Christini et al demonstrated certain advantages associated with the deposition of the barrier layer (strike) prior to the composite layer.
Feldstein in U.S. Pat. Nos. 4,358,922 and 4,358,923 demonstrated the advantages of utilizing a metallic layer above the composite layer. The overlayer is essentially free of any particulate matter. Spencer in U.S. Pat. No. 4,547,407 demonstrated the utilization of a mixture of dual sized particles in achieving improved smoothness of coating, Feldstein et al in U.S. Pat. Nos. 4,997,686; 5,145,517; and 5,300,330 demonstrated the utilization of particulate matter stabilizers in the deposition of uniform stable composite electroless plating and various associated benefits. Parker in U.S. Pat. No. 3,723,078 demonstrated the codeposition of refractory metals and chromium along with composite electroless plating.
Helle et al in U.S. Pat. Nos. 4,098,654 and 4,302,374 have explored special surfactant compositions in the preparation of stabilized PTFE dispersions and their subsequent utilization in electrolytic plating.
Kurosaki et al in U.S. Pat. No. 3,787,294 proposed cationic stabilizers for graphite fluoride be used in electroplating with specific attention focused upon surfactants having a C--F bond in their structure.
Brown et al in U.S. Pat. No. 3,677,907, demonstrated the utilization of surfactants also having a C--F bond in their skeleton used in combination with PTFE electrolytic codeposition.
Henry et al in U.S. Pat. No. 4,830,889, demonstrated the utilization of a cationic fluorocarbon surfactant along with a non-ionic fluorocarbon surfactant for the codeposition of graphite fluoride in electroless plating baths.
Feldstein et al in U.S. Pat. No. 5,389,229, demonstrated the use of "frozen states" to overcome the limited shelf-life associated with certain dispersions before their use in plating applications.
The above patents and applications reflect the state of the art and they are included herein by reference.
In pending application Ser. No. 08/295,563, it has been demonstrated that plated articles can be rejuvenated readily without damage to the base substrate and the parts can be used for repeated cycles. This capability is achieved by the deposition of an Indicator Layer and thereafter the functional layer. As the functional layer is damaged and/or worn the Indicator Layer is exposed alerting the operator to change the parts from it's environmental use. Though this development is most useful, certain limitations are noted.
1. At least two layers are required in the overall metallized structure, i.e., an Indicator Layer and thereafter the functional layer.
2. When rejuvenating the plated articles the remnants of the functional layer and indicators must be removed (stripped) before the new generation can be coated.
Accordingly, though the features for the Indictor Layer are most desirable, greater simplicity is now proposed. Specifically, the current invention incorporates the indicator Layer along with the functional coating (layer) all in one layer. Therefore, in the current invention a continuous signal will be noted from the plated part until the functional layer (including the signaling particles) is worn off. At which time, the signal will cease in the worn region. Upon the cessation of the signal rejuvenation of the part should take place for the repeated usage.
The finely divided particulate matter (indicator particles) referred herein are particles comprised of atoms or molecules that absorb photons of electromagnetic radiation and reemit the absorbed energy by the spontaneous emission of photons which, however, are not the same energy as absorbed photons or the same wavelengths. The phenomenon is generally referred to as luminescence, having light emitting properties.
Luminescence is further classified into fluorescence and phosphorescence. If the emitted radiation continues for a noticeable time (generally between 10.sup.-4 -10.sup.-9 seconds) after the incident radiation is removed, the process is referred to as fluorescence. Specific examples of such materials include pore solids of known chemical composition or naturally occurring metals.
It is apparent from the above that a wide variety of materials can usefully be employed as the Indicator particles.